Body of large size. Prostomium rounded, with a small conical tip. Without eyes. Thoracic segments bi-annular and partly tessellated. Eleven segments with annulate and partly tessellated. Eleven segments with capillary dorsal and ventral setae. First abdominal dorsal tori very small, connected across the dorsum by a low transverse fold: posteriorly they become obsolete. First abdominal ventral tori ending in a sharp upper process which decreases in size farther back. Gills retractile and usually obscured anteriorly; on the middle and abdominal segments they become conspicuous bushy tufts, composed of numerous (about 20-30) filaments arising from the posterior end of the dorsal tori, or posteriorly, when the tori become obsolete, replacing them. A pair of large genital pores on the first 9 abdominal segments.